In the field of semiconductor devices, in order to ensure effective chip design and layout, effective and reliable characterisation of capacitive structures is required. Such capacitive structures may include, by way of example, coupling capacitance between metal lines, gate capacitance of transistors, diode capacitance, capacitive sensor capacitance, etc. In order to achieve such characterisation of capacitance structures, it is known to use test structures, wherein a prototype chip having one or more desired capacitive structures of an integrated circuit (IC) chip to be characterised is manufactured, and the capacitances of the test structures are measured. The capacitance measurement results can then be used to analyze if fabrication of silicon for the desired capacitive structures is within target, for debug of any related issues in the device's circuitry, for readout of a capacitive sensor, etc.
Conventional techniques for measuring the capacitances of the test structures comprise applying voltage pulses to the test structures, and measuring current flow through the test structures. Average current measurements may then be used to calculate the capacitance of the test structures: C=I/Vf.
However, the continued advances in semiconductor fabrication processes have lead to increasingly smaller transistor architectures, resulting in increasing sensitivity to on-die capacitances such as parasitic capacitances, coupling capacitances, etc. As such, currents in the range of pico-amps (pAs) and below are required to be measured using conventional techniques in order to enable sufficiently sensitive characterisation of the on-die capacitances. In order to measure such small currents, a Parametric Analyser is required. Standard automated test equipment (ATE) often does not comprise an integrated Parametric Analyser. Even where a parametric analyser is integrated into the available ATE, the use of a Parametric Analyser to enable such accurate current measurements requires numerous averaging techniques, resulting in excessively long measurement times.